Type M-x cd to change directory to the location of the program you wish to debug.
Type M-x pdb. You’ll be prompted with Run pdb (like this): pdb. Enter the name of the program (e.g. test.py).
At the (Pdb) prompt, type help to learn about how to use pdb.
Alternatively, you can put
import pdb
pdb.set_trace()
right inside your program (e.g. test.py). Now type M-x shell to get a shell prompt. When you run your program, you’ll be dumped into pdb at the point where pdb.set_trace() is executed.